In optical communication, transmission capacity has been increased by using methods such as time multiplexing or wavelength multiplexing for realization of real-time transmission of multi-media information (particularly, image information). The signal form used for the real-time transmission is basically a time signal. Because of the transmission capacity increase, it is necessary to perform conversion (encoding) of information to be transmitted into time signals and expansion (decoding) of the information converted into the time signals at a ultra-high speed. For this reason, there has been proposed a “space-to-time-to-space signal processing method” which realizes ultra-fast conversion of signal form between time signal and two or more dimensional space signal such as image information. However, this space-to-time-to-space signal processing method has a problem that must be solved in time-to-two-dimensional space signal conversion technology.
Various methods have been proposed as the method for realizing ultra-fast conversion of signal form between time signal and space signal. However, although the conventional methods are capable of carrying out ultra-fast conversion into one-dimensional space signal, some of them basically need to perform active scanning for conversion into two or more dimensional space signal and thus have a limitation in transformation speed. On the other hand, there are some methods that do not need to perform active scanning, but space signal converted by such methods cannot be observed with any ultra-fast light-receiving device available today.